1. Field of the Invention
This invention relates to blood collecting and separating tube assemblies and more particularly to puncturable stoppers used to form a vacuum-tight and liquid-tight seal within the open end of a blood collecting and separating tube.
2. Prior Art
Evacuated tubes have been used to collect and separate blood for some 20 years. The conventional tube assemblies include a cylindrical container or tube having a closed end and an open end vacuum sealed by means of a removable needle-pierceable stopper or closure. Typically blood is withdrawn from a patient by first puncturing a vein with one end of the double-ended needle and then while firmly securing the housing holding the needle, pushing the needle pierceable closure of a collection tube against the other end of the needle until the closure is pierced. The partial vacuum within the collection tube results in siphoning or withdrawing blood into the tube. After the desired volume of blood is drawn into the tube, the needle is withdrawn from the patient. An example of a conventional blood collecting and separating tube is described in U.S. Pat. No. 2,460,641.
The standard venipuncture procedure is usually accomplished with the stoppered end of the container being held downwardly. Accordingly, as blood is siphoned into the tube, the blood will rest against the inner surface of the stopper, that is, at the bottom end of the stopper. After venipuncture, it has been found that with known container assemblies a small portion of the blood remains attached to the bottom end of the stopper and also between the stopper and container walls.
The major failing of the standard stopper, from the user standpoint, is its retention of a substantial portion of clotted blood or cells at the stopper-container wall juncture even upon completion of the centrifugation of the blood. This failing makes it highly desirable, if not essential, to remove the stopper before centrifugation and clean (using a swab or stick) the clot or cells from the top inside wall of the tube.
Merely removing the stopper without cleaning the residual ring-clot or cells will not overcome the problem, since centrifugal force does not remove the unwanted attachment of clot or cells from the tube wall because of the drying onthe wall that begins to occur just after the stopper is removed or "popped". This drying and adhering of clot or cells on the tube wall has been found to be aggravated during centrifugation both by turbulent air action and by rising temperatures within the centrifuge, throughout the duration of the spin, which is typically, eight to twelve minutes. Cleanliness of the tube wall after centrifugation is highly desirable because most serum is poured from the tube, and attached cells can thus be eluted by the pouring of the serum or plasma.
Under present practices requiring the removal of the stopper prior to centrifugation, a period of up to three hours may elapse between centrifugation and serum or plasma utilization, during which time the blood sample is open to the atmosphere and evaporation of gaseous blood constituents may take place. The net result may be an increase in the apparent concentration of some blood constituents and a decrease in the apparent concentration of the gaseous constituents, which produces a deviation from the true clinical values of serum or plasma chemistries for the patient in question.
Also while the unstoppered tube is standing in a rack waiting to be analyzed, particulate matter and other airborne contaminants, as well as splashed reagents or splashed serum from other tubes (occurring when tubes are hastily put into a common rack), can readily contaminate the blood sample prior to analysis.
The over-riding concern with blood collecting and separating tube assemblies which require stopper removal is, however, the potential hazard to laboratory personnel. The removal of the stopper, the rimming with a stick or swab to remove the ring clot, the aerosol effect created by the centrifuge rotation, and the possibility of accidental spillage all jeopardize the well-being of laboratory workers.
Also since cells trapped between the stopper and the tube walls may be ruptured when the stopper is removed, which results in the exuding of lactic dehydrogenase (LDH), falsely elevated LDH levels in the serum or plasma analysis may be produced.
Accordingly, it is an object of this invention to provide a stopper for use in combination with a blood collecting and separating container which will overcome the disadvantages of prior stoppers.
Also it is an object of this invention to provide a stopper which is easily insertable and removeable from a blood collecting and separating tube, and yet which maintains an adequate vacuum-tight seal for a prolonged storage time.
It is a further object of this invention to furnish a stopper of such a construction that the entire circumferential junction of the stopper and tube inner face is maintained in a fluid tight configuration to preclude the possibility of blood portions from being lodged between the stopper and tube wall.
Another object of this invention is to provide a stopper having a bottom axial cavity configuration which causes blood adhering within the cavity to flow from the cavity during an angle-head mode of centrifugation.
It is also a major object of this invention to provide a stopper suitable for use with a closed-system blood collecting and separating assembly having either a gel-like barrier material initially positioned at the closed end of the tube, such as the assembly disclosed in U.S. Pat. No. 3,852,144 or a resilient spool barrier means initiallly positioned adjacent the stoppered end of the tube, as described in U.S. Pat. No. 3,814,248. The closed-system assembly may be used to collect blood, centrifugally separate blood into at least two phases, and automatically partition the separated phases with the gel-like barrier material and/or the spool. To assure that the separated phase above the barrier, which may be serum or plasma, is not contaminated before or during pour-off of such phase, it is important that no blood constituents remain in the vicinity of the juncture of the stopper and tube wall or in an axial cavity in the bottom of the stopper upon completion of centrifugation, and the stopper of the present invention not only inhibits the formation of ring clotting but also facilitates the removal of such constituents during centrifugation.